1. Field of the Invention
The present invention relates to an X-ray protector that turns a power supply circuit OFF when a voltage exceeding a preset voltage is applied to a Braun tube, i.e., a cathode ray tube (CRT), of a TV receiver.
2. Prior Art
FIG. 3 is a block diagram showing one example of a circuit including a prior art X-ray protector of a TV receiver. In the figure, reference numeral 32 depicts a connection plug to be connected to an AC power source, and reference numeral 35 depicts a power supply circuit that supplies electric power in order to operate a Braun tube 38, i.e., CRT. In addition, a relay circuit 33 is connected between the plug 32 and an input terminal of the power supply circuit. The relay circuit 33 is arranged to be turned ON or OFF by an input of a control signal output from a microcomputer 31.
The electric power output from the power supply 35 is input to a primary winding of a flyback transformer 36, and a voltage in proportion to a voltage applied to the primary winding is induced in a high-voltage winding, and the voltage in the high-voltage winding is rectified to be positive potential and pulsed shape and is applied to the Braun tube 38. Furthermore, a voltage in proportion to the voltage applied to the Braun tube 38 is induced in a detection winding. After that, a signal based on the voltage generated in the detection winding is input, via a detection circuit 39, to an input port 31a of the microcomputer 31 so that the voltage applied to the Braun tube 38 can be determined by the microcomputer 31.
In the above-described X-ray protector, when a voltage exceeding a predetermined voltage is applied to the Braun tube 38 for some reason or other, the microcomputer 31 determines that situation through the signal input to the input port 31a and turns the relay circuit 33 OFF, thereby preventing an emission of X-rays exceeding a permissible dose caused by the situation where a voltage higher than a predetermined voltage is continued to be applied to the Braun tube 38.
In an assembly process of such as a TV receiver or the like, the test of the X-ray protector operation is usually conducted in order to determine whether an X-ray protector functions normally or not. When conducting such an operation test, an output voltage of the power supply 35 is adjusted so that a voltage exceeding a voltage in the case of normal operation is applied to the Braun tube 38, and then the test is conducted as to whether the microcomputer 31 can function to turn the relay circuit 33 OFF normally.
However, the applying of an excessive voltage exceeding a voltage applied to normally operate a Braun tube causes generation of X-rays exceeding a permissible dose from a Braun tube, and this is not preferable for the workers of this test in view of their health. Further, a Braun tube can be damaged by the application of the excessive voltage.
On the other hand, a test of an X-ray protector's operation may be conducted without raising the voltage to be applied to a Braun tube. In this case, comparison standard data for testing are set in a microcomputer, whereby a relay circuit can be turned OFF depending on the basis of the comparison between the comparison standard data and a detection value of the voltage to a Braun tube. However, in order to operate the relay circuit on the basis of the detection value derived from the testing by setting comparison standard data for testing in a microcomputer, it is inevitable that a control procedure for testing utilizing a microcomputer becomes complicated, thereby complicating a control program of a microcomputer.